Numerous dynamic force generators with unbalanced masses are known.
An unbalanced mass is a mass that is off-centre relative to the rotation axis of the dynamic force generator.
In this type of dynamic force generator, the unbalanced masses are set in rotation to generate a centrifugal force, the resultant of which makes it possible, in practice, to counteract a vibration generated in a structure.
In particular, in the field of aircraft, the engines generate vibrations, which we aim to decrease or at least limit.
This is notably the case for rotating-wing aircraft (helicopters). In fact, the rotor (main or secondary as applicable) providing lift for the helicopter generates many vibrations, notably on the fuselage, that it is necessary to counteract.
For these applications in particular, the use of a dynamic force generator with at least two unbalanced masses is attractive as the generators are relatively light and compact, compared to other classes of dynamic force generators.
Documents U.S. Pat. No. 5,005,439, EP 2 926 026 or U.S. Pat. No. 9,073,627 propose various designs of dynamic force generators with at least two unbalanced masses.
However, there are constant efforts to improve dynamic force generators of this type, notably to reduce their weight, make them more compact (reduced overall dimensions), but also to improve their service life.